Detectives have been given more time to quiz two men they arrested on suspicion of randomly attacking strangers in a stabbing spree.
Four people were injured, two critically, when they were knifed from behind while walking in the Edmonton area of north London over the weekend.
Police believe that a single male suspect who may have mental health issues was acting alone in the attacks.
Scotland Yard said that the two men arrested on suspicion of GBH remained in custody after officers were given extensions to interview them into Tuesday.
One, a man believed to be in his 40s, was arrested at a home in Edmonton and the other was arrested in Fore Street.
The Metropolitan Police said a 45-year-old woman and a 23-year-old man remained in a critical condition in hospital on Monday night.
A Section 60 order was put in place to allow officers in Edmonton to stop and search anyone to prevent further violence. This was to last until 1.50am on Tuesday
Police urged people to stay vigilant after the string of “senseless and cowardly” attacks over 15 hours.
Officers said there is nothing to suggest the incidents were terror related.
The suspect is described as a black man, approximately 6ft 3ins tall, of skinny build and wearing dark clothing.
The 45-year-old woman became the first victim when she was stabbed once in her back at about 7pm on Saturday in Aberdeen Road.
The final attack occurred at about 9.40am on Sunday in Brettenham Road where officers found a 29-year-old man with a stab injury to the back.
